The present invention relates to a device for checking and calibrating high precision inclinometric sensors. In particular, highly sensitive inclinometric sensors need very precise calibration in order to best exploit their potential resolution capabilities. The potential precision of most instruments is affected by noise caused by the sensor and by the electronics, and thus far the existing calibration devices available on the market have not been able to solve the problem of an optimal calibration.
Inclinometers measure variations in the gradient of the surface whereto they are fixed and are used for checks especially in the industrial, geotechnical and geophysical fields. In the industrial field, these instruments are used to verify various types of alignments and to position instruments with precision, whilst in the geotechnical field they are used to monitor the deformation state whereto particular structures such as foundations, bridges, dams, tunnels are subjected. In the geophysical field they are essentially used to monitor soil deformations associated to possible events of various kinds such as slope instability, tectonic movements, movements of volcanic origin. Inclinometric sensors essentially use as a vertical reference a pendulum or an electrolytic bubble with respect to which they measure inclination variations.
Nowadays the most widely used inclinometers are those with electronic sensors whose principle is essentially based on the equilibrium position assumed by an electrolytic bubble suspended inside a fluid-filled container. Electronic sensors detect resistance variations measured through the variations in position of the electrolytic bubble with respect to electrodes integral with the container. The sensors are usually set to measure inclinations along two orthogonal axes in order to obtain a spatial representation (module and direction) of the inclination vector. These instruments are generally able to reach high theoretical precision (resolution in the order of 0.1-0.01 microradians), but under ordinary conditions their limit consists of the fact that they are hardly able to exploit this potential. The noise effects induced by the environment are considerable and they mainly pertain to temperature variations that can create noise both in the sensor and in the electronics. A further problem pertains to the linearity of the response by the instrument which is not necessarily maintained along the entire measurement range. These aspects are not always analysed in detail by manufacturers which usually do not provide precise calibration card and the detailed procedures of any calibration tests which may have been conducted.
The laboratory evaluation of the exact noise caused by thermal variations and the verification of the correct instrumental response, in addition to a check of the regular operation of the instrument, would also allow a more adequate evaluation of procedures for filtering xe2x80x9cspuriousxe2x80x9d effects not connected to real variations, thereby fully exploiting the potential of the instrument.
The aim of the present invention is to eliminate the drawbacks mentioned above, realising a device for checking and calibrating high precision inclinometric sensors that obtains a correct calibration of these instruments with precision of less 0.1 xcexc/m.
Normal calibration tables available on the market use an adjustment system comprising a micrometer with good mechanical characteristics, but with a resolution that is at least an order of magnitude poorer. The solution of adding to a table of this kind a set of leverages to reduce the travel of the micrometer is unsatisfactory because the system would still be limited by the mechanical couplings, play, friction, etc., which would make it very difficult to drop below a tenth of a micron.
In addition to the mechanical aspects, the fundamental problems with normal calibration tables are:
i) during the calibration time they cannot distinguish possible real effects, i.e. actual gradient changes by induced the real adjustment on the plate, from fictitious effects, i.e. induced by the surrounding environment;
ii) they are also unable to discriminate to what extent thermal variations affect the sensor as noise or may influence possible undesired movements of the plate.
Therefore, in accordance with the present invention, a calibration device has been devised and realised that makes no direct use of mechanical apparatuses to adjust and verify the inclination, but that is based instead on the different inclination that a floating object assumes as its baricentre varies.
The invention, as it is characterised by the claims that follow, solves the problem of providing a device for checking and calibrating high precision inclinometric sensors, which from a general point of view is characterised in that it comprises:
a planar base body of substantially quadrangular shape, made of highly rigid material, set to float on the mercury placed inside a tank;
a pair of micrometric positioning means of known weights, situated in proximity to concurrent edges of the base body, on the respective orthogonal axes of symmetry of the base body, able to allow varying the baricentre and the inclination on the mercury of the base body by a value determined by the variation of the applied moment;
a pair of screws for adjusting the zero point, situated on said base body, in positions respectively opposite to said pair of micrometric positioning means of known weights, such as to be able to act on the axes of symmetry to be positioned within the whole measurement range of the sensor;
a seat situated centrally with respect to the base body for positioning an inclinometric sensor centrally on said axes of symmetry.
Further features and advantages of the invention shall be made more readily apparent from the detailed description that follows, of a preferred embodiment illustrated purely by way of non limiting example in the accompanying drawings.